On March 7, Saudi Arabia took the extraordinary step of declaring the Muslim Brotherhood a terrorist organization, on par with Hezbollah and al Qaeda. The move came just two days after the kingdom, together with the United Arab Emirates and Bahrain, withdrew its ambassador from Qatar because of Qatar’s alleged support of Brotherhood interference in internal politics. Although Saudi Arabia’s dislike of Brotherhood political activities abroad is well known, for decades the kingdom has tolerated (and sometimes even worked with) the local Saudi branch of the Brotherhood. Its sudden reversal is an expression of solidarity with its politically vulnerable allies in the region and a warning to Sunni Islamists within its borders to tread carefully.

This story goes back to the Arab Spring, when Egyptian President Hosni Mubarak, Saudi Arabia’s longtime ally, was ousted, and Egypt elected Mohamed Morsi, a Muslim Brotherhood­–linked politician, to fill his shoes. Riyadh feared that the group, now empowered, would try to export the Egyptian revolution regionwide, calling for action against the House of Saud and displacing Saudi’s friends and allies such as the UAE. Those fears were not entirely unfounded.

In Saudi Arabia, members of the Muslim Brotherhood had been at the forefront of the Awakening movement, a push in the early 1990s for political change in response to alleged Saudi government corruption and the basing of U.S. troops in the country. But, as the political science professor Stéphane Lacroix documents in his book Awakening Islam, most members of the Saudi Muslim Brotherhood had quickly fallen into line once the regime began to arrest or sanction its leaders. The Saudi Brotherhood simply had too much to lose: its members helped build the Saudi state and occupied important positions in the religious and educational establishment.

That détente ended with the Arab Spring, when a number of prominent Islamists added their names to a 2011 petition calling for political reforms in the kingdom. They also obliquely criticized the lack of political freedom in